Self buffers

Sodium tetraborate, Na2B407, dissociates to form an equimolar concentration of metaboric acid, HBO2, and metaborate ion, B02, estabhshing such a reproducible hydrogen ion concentration in the solution that this material is used as a primary standard in pH measurement. (This interpretation is oversimplified account should also be taken of the tendency of boric acid and borate ion to form concentration-dependent polymers.) Another example is potassium tetroxalate which is an equimolar mixture of potassium hydrogen oxalate and oxalic acid. 

It is convenient to designate as self buffers substances which possess this ability to act as buffers. They are very 

Piperazine phosphate monohydrate, C4 Hi 2 N2 HPO4 H2 O, is a very good self buffer (pATa values of piperazine 5.333, 9.731 relevant pATa value of phosphoric acid 7.198 at 25° C) and it has been proposed for use as a pH standard. Measured pH values for an 0.02m solution from 0 to 50° C are given in Table 2.5. For an 0.05m solution the pH values should be increased by 0.009. 

Ampholytes (zwitterions) include an extensive range of substances that could be used as self buffers. Table 2.6 gives a list of isoionic ampholytes proposed for use as buffers in protein fractionation in a natural pH gradient (Svensson, 1962). Solutions of these substances in water have pH values close to the listed value of pi and when p7 - pA i is less than 1.5 they can be considered to be self buffers. 

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Rate of hydrolysis Slow with water but fairly rapid with strong acids and alkalies self-buffering at pH 4.5. Autocatalytic below pH 4, because of presence of HCN. Half-life, 8.5 h at pH 7 (20°C) 7 h at pH 4-5. The rate of hydrolysis is increased by the presence of phosphate. 

Sodium perborate has been recommended for the oxidation of alkenyldialkoxyboranes to aldehydes. In particular, the reagent avoids the formation of possibly hazardous 2 1 aldehyde-4iydrogen peroxide adducts as well as C—C bond cleavage. Sodium percarbonate is an air-stable solid, inexpensive and self-buffered, that appears to be a promising oxidant. ... 

The use of buffer solutions is usually advisable for accurate control of the pH of solutions used in spectrophotometric titrations, since the solutions will usually be so dilute (because of the relatively high protein or peptide absorptivity) as to offer little self-buffering. The usual buffers for the pH range from 9 to 13, i.e., borate, glycinate, phosphate, lysine, -aminocaproic acid, etc., are generally transparent through the 2950 A phenolate band. Buffer systems composed of piperidine (pK, 11) and its hydrochloride have been used to avoid the use of multivalent anions in the spectrophotometric titration of ribonuclease (Klee and Richards, 1957), but no other advantage is apparent for this system. 

Other investigators (14, T3) contend that the bacteria biologically oxidize the ferrous to the ferric state as sulfate, which in turn attacks the metal sulfides ores, resulting in both the dissolution of the metal and the oxidation of the sulfide. In the process the ferric iron reduces back to the ferrous state. An increase in the pH causes the basic ferric sulfate to precipitate (self-buffering action) with corresponding release of sulfuric acid. This has the cumulative effect of increasing the acidity of the mine water. 

Self-buffering, stable catalyst Catalyst-solvent phase can be recovered and re-used... 

Figure 12-7. Degradation of cotton with self-buffered hypochlorite solution (3 g/1 av. Cl ) after 5 h treatment [24],...

In the laboratory, RH in relatively small containers (typically a desiccator) can be controlled by the use of saturated salt solutions. Some data over a wide range of humidities at temperatures of 22.8, 30.0 and 37.8 °C have been given by Wink and Sears. These are self-buffering, in that, loss of water vapour results in evaporation from the liquid, and precipitation of salt. Conversely, the addition of liquid water causes some salt to be dissolved. It is important that salt crystals are present at all times. 

Dediazoniation reactions rates were carried out in NaOAc and NaPAA at various pH s. NaOAc solutions are self buffered, and NaPAA solutions were buffered with 1 x 10" M HEPES. Reactions were monitored at 40 + 0.1 C,... 

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